Researcher Jon Ayres, professor of environmental and occupational medicine at Aberdeen University, said: “These findings confirm the dramatic effect that smoking cessation in pubs and bars can have on air quality. This can only be to the benefit of bar staff and customers alike.”

The researchers measured the air quality inside 41 Scottish pubs in the two months prior to the ban last year and again in May and June 2006 and assessed the respiratory health of 371 bar workers in Scotland.

Scottish health minister Andy Kerr said: “Exposure to second-hand tobacco smoke was one of the main problems the smoking ban was designed to tackle. This research proves it’s working.”

However, the complete results of the study will not be available until the end of the year.